NK cells are large granular lymphocytes that help control infections and tumors and regulate autoimmune responses. Once activated, NK cells have both cytotoxic and cytokine-secreting effector functions. NK cells employ Fas, TRAIL, and secretion of perforin and granzyme B to induce apoptosis or lysis of distressed somatic cells. NK cells also produce cytokines and are a major source of IFNγ at early times after viral and bacterial infections. Secreted IFNγ enhances cytotoxicity against tumor cells, induces CD4 Th1 differentiation, stimulates antiviral responses, and activates macrophages to become more bactericidal to intracellular pathogens.
Stimulation of innate immune responses can be used to treat a variety of disorders. In addition, stimulation of innate immune responses can be used to improve adaptive immune responses to certain agents and/or vaccines to improve responsiveness to these agents.